Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/06—Lubrication
  • F04D29/063—Lubrication specially adapted for elastic fluid pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D19/00—Axial-flow pumps
  • F04D19/02—Multi-stage pumps
  • F04D19/04—Multi-stage pumps specially adapted to the production of a high vacuum, e.g. molecular pumps
  • F04D19/042—Turbomolecular vacuum pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
  • F04D29/056—Bearings
  • F04D29/058—Bearings magnetic; electromagnetic
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
  • F04D29/056—Bearings
  • F04D29/059—Roller bearings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
  • F16C33/30—Parts of ball or roller bearings
  • F16C33/66—Special parts or details in view of lubrication
  • F16C33/6637—Special parts or details in view of lubrication with liquid lubricant
  • F16C33/664—Retaining the liquid in or near the bearing
  • F16C33/6648—Retaining the liquid in or near the bearing in a porous or resinous body, e.g. a cage impregnated with the liquid
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C19/00—Bearings with rolling contact, for exclusively rotary movement
  • F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
  • F16C19/04—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly
  • F16C19/06—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly with a single row or balls
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C2360/00—Engines or pumps
  • F16C2360/44—Centrifugal pumps
  • F16C2360/45—Turbo-molecular pumps

Definitions

• This invention relates to a vacuum pump, and in particular to the lubrication of rolling bearings used to support the impeller of a vacuum pump.
• Vacuum pumps typically comprise an impeller in the form of a rotor mounted on a shaft for rotation relative to a surrounding stator.
• the shaft is supported by a bearing arrangement comprising two bearings located at or intermediate respective ends of the shaft.
• One or both of these bearings may be in the form of rolling bearings.
• the upper bearing is in the form of a magnetic bearing
• the lower bearing is in the form of a rolling bearing.
• a typical rolling bearing comprises an inner race fixed relative to the shaft, an outer race, and, located between the races, a plurality of rolling elements for allowing relative rotation of the inner race and the outer race. To prevent mutual contacts between the rolling elements, they are often guided and evenly spaced by a cage. Adequate lubrication is essential to ensure accurate and reliable operations of rolling bearings.
• the main purpose of the lubricant is to establish a load-carrying film separating the bearing components in rolling and sliding contact in order to minimise friction and wear. Other purposes include the prevention of oxidation or corrosion of the bearing components, the formation of a barrier to contaminants, and the transfer of heat away from the bearing components.
• the lubricant is generally in the form of either oil or grease (a mixture of oil and a thickening agent).
• Vacuum pumps using oil-lubricated bearings require an oil feeding system for feeding oil between the contact areas of the bearing, which enables the oil to perform cooling as well as lubrication and thereby permit the bearings to run at a faster speed.
• Turbo-molecular pumps have traditionally used a wicking system for supplying oil to a rolling bearing.
• a felt wick partially submerged in an oil reservoir feeds oil to a conical "oil feed" nut mounted on the shaft. With rotation of the pump, oil travels along the conical surface of the nut to the bearing. The oil passes through the bearing and is returned to the reservoir.
• a pressure differential may be generated across the oil reservoir which causes outgassing in the reservoir.
• outgassing can cause oil to escape from the bearing cavity and contaminate the pump.
• Vibrational excitation during use of the pump may additionally promote the nucleation of bubbles contributing to oil loss.
• outgassing may cause an excess of oil to be transferred to the oil feed nut which may stress the bearing.
• the present invention seeks to reduce the effect of outgassing in vacuum pumps.
• the present invention provides vacuum pump comprising a bearing and a lubricant supply system for lubricating the bearing; the lubricant supply system comprising: a lubricant reservoir comprising a reservoir matrix for receiving a lubricant; a lubricant transfer arrangement in contact with the reservoir matrix for transferring lubricant from the reservoir matrix to the bearing, the reservoir comprising a reservoir enclosure for locating the reservoir matrix in position relative to the lubricant transfer arrangement; wherein the reservoir comprises a plurality of contact regions at which the reservoir matrix is in contact with the reservoir enclosure for locating the reservoir matrix in position relative to the lubricant transfer arrangement and a plurality of spacing regions between respective contact regions at which the reservoir matrix is spaced apart from the reservoir enclosure for receiving gas and lubricant foam caused by outgassing in the lubricant in the reservoir matrix.
• Figure 1 shows a section of a vacuum pump
• Figure 2 shows a section of a lubricant supply system of the vacuum pump shown in Figure 1 ;
• Figure 3 shows a cross-section of a known lubricant supply system;
• Figure 4 shows the known lubricant supply system in use
• Figure 5 shows a radial cross-section of an improved lubricant supply system taken along line V-V of Figure 6;
• Figure 6 shows a section of the lubricant supply system taken along line VI-VI of Figure 5;
• Figure 7 shows the arrangement of Figure 6 in use.
• Figure 8 shows a section of an alternative embodiment of the lubricant supply system taken along line V-V of Figure 6.
• Figure 9 shows a section of an alternative embodiment of the lubricant supply system taken along line V-V of Figure 6.
• Figure 10 shows a section of an alternative embodiment of the lubricant supply system taken along line V-V of Figure 6.
• Figure 1 1 shows a further additional embodiment of the lubricant supply system taken along line X-X of Figure 6.
• Figure 12 a/b show a side and plan view of further alternative
• a cross-section of a vacuum pump 10 comprising a pumping arrangement driven by a shaft 12.
• the illustrated vacuum pump is a turbomolecular vacuum pump comprising a turbomolecular pumping mechanism 14 and a molecular drag pumping mechanism 16.
• the turbomolecular pumping mechanism comprises a plurality of rotor blades 18 mounted on, or integral with, the shaft 12.
• the molecular drag pumping mechanism 16 is in the form of a Holweck pumping mechanism, and comprises one or more cylinders 20 mounted on the shaft 12.
• the molecular drag pumping mechanism may alternatively comprise a Siegbahn mechanism comprising rotating discs.
• an aerodynamic pumping mechanism downstream of the molecular drag pumping section comprising a regenerative mechanism.
• the shaft is rotated about longitudinal axis 22 by a motor 24 to drive the pumping arrangement.
• the shaft 12 is supported by a bearing arrangement comprising two bearings which may be positioned either at respective ends of the shaft as shown or alternatively intermediate the ends.
• a rolling bearing 26 supports a first portion of the shaft 12 and a magnetic bearing 28 supports a second portion of the shaft 12.
• a second rolling bearing may be used as an alternative to the magnetic bearing 28.
• the rolling bearing 26 is provided between the second end portion of the shaft 12 and a housing portion 30 of the pump 10.
• the rolling bearing 26 comprises an inner race 32 fixed relative to the shaft 12, an outer race 34, and a plurality of rolling elements 36, supported by a cage 38, for allowing relative rotation of the inner race 32 and the outer race 34.
• the rolling bearing 26 is lubricated by a lubricant supply system 40 to establish a load-carrying film separating the bearing components in rolling and sliding contact in order to minimise friction and wear, as shown in Figures 2 and
• the lubricant supply system 40 comprises a liquid lubricant reservoir 42, which surrounds an axis of rotation 22 of the shaft 12.
• the reservoir 42 comprises a reservoir matrix formed in this example by a stable fibrous annular substrate surrounding a central bore 44 of the reservoir 42, and having voids (e.g. pores) within which oil, or other liquid lubricant, is stored.
• the reservoir 42 also comprises at least one and preferably a multiplicity of projections 46 which project into the bore 44.
• the projections may be made from a similar fibrous material to the reservoir matrix, such as felt, or by filaments forming brushes.
• the projections are held by the reservoir 42 so that they are in contact with a tapered feed nut 48 mounted on the shaft 12 and located within the bore 44 of the reservoir.
• the end of the tapered nut 48 located adjacent the bearing 26 has an external diameter which is approximately equal to the internal diameter of the cage 38 of the bearing.
• the projections are located approximately mid way along the axial length of the reservoir 42.
• this location is arbitrary and the axial location of the projections may vary from one vacuum pump to another.
• the projections or fingers may be omitted and in this case, the annular body of the reservoir matrix may be located in contact with the lubricant transfer arrangement 48, so that an interior surface contacts the oil feed nut 48 over at least a portion of the axial extent of the reservoir matrix.
• Lubricant can therefore be transferred from the interior surface of the matrix directly to the lubricant transfer arrangement (oil feed nut 48).
• the reservoir matrix may extend radially inwardly to a greater extent at one axial portion, for example a middle portion, to form a projection 46, to contact the oil feed nut 48.
• the matrix may be formed by more than one component stacked one on another in layers and one of the layers may project further inwards than the layers adjacent to it in order to form a projection 46 to contact the oil feed nut.
• the lubricant is drawn along the projections 46 and is deposited onto the feed nut 48 as it rotates. This lubricant is transferred axially along the feed nut to the cage 38 of the bearing 26 by virtue of the taper on the nut and the rotation of the nut.
• Figure 3 is a cross-section taken along line Ill-Ill in Figure 2 looking towards the bearing 26 and shows a prior art lubricant supply system.
• the external surface 50 of the reservoir matrix 42 is in contact with the internal surface 52 of the housing portion 30 throughout the circumference of the surfaces.
• the reservoir material is to some extent resilient and its shape is at least partially formed by its location within the housing portion 30, which acts as a reservoir enclosure containing the matrix.
• the internal surface of the housing portion 30 has a circular cross-section which is uniform in the axial dimension forming a cylindrical surface.
• the external surface similarly has a circular cross-section of the same radius, or marginally larger, than the radius of the internal surface of the housing 30.
• FIG. 4 is a view similar to Figure 2 and shows the known lubricant supply system shown in Figures 2 and 3 in use filled with a lubricant.
• the reservoir matrix 42 is constrained radially in the bore of the reservoir enclosure 30 and also axially by a further housing portion 54 underneath the reservoir in the illustrated orientation of the pump. During pumping, or when there is a differential pressure across the reservoir produced by initial evacuation by a primary pump, outgassing occurs in the reservoir matrix 42 causing trapped gas and
• Figures 5 to 12 show an improved lubricant supply which at least mitigates the problems caused by outgassing and the generation of lubricant foam.
• Figure 5 is a view similar to Figure 3 and shows a cross-section through the lubricant supply system taken along the line V-V in Figure 6.
• Figure 6 is a view similar to Figures 2 and 4 taken along line VI-VI in Figure 5.
• a view taken along line 11-11 in Figure 5 would show an arrangement which is the same as the prior art in Figure 2 because the section is taken through the contact portions 64, as described in more detail below.
• the lubricant supply system 60 comprises a reservoir matrix 62 for receiving and storing a lubricant, such as oil, for transfer by the lubricant transfer arrangement from the reservoir matrix to the bearing 26.
• the reservoir matrix is located in position relative to the lubricant transfer arrangement by the housing portion 30 and the axial housing portion 54, which form together a reservoir enclosure.
• the reservoir comprises a plurality of contact regions 64 at which the reservoir matrix 62 is in contact with the reservoir enclosure 30 for locating the reservoir matrix in position relative to the oil feed nut 48 and a plurality of spacing regions 66 between respective contact regions at which the reservoir matrix is spaced apart from the reservoir enclosure for receiving a lubricant foam caused by outgassing in the lubricant in the reservoir matrix.
• the reservoir enclosure 30, 54 may comprise locating means which project radially inward from the enclosure wall to contact and locate the reservoir matrix.
• the spacing regions may be substantially continuous around the periphery of the matrix.
• the spacing regions 66 provide an escape, or expansion, volume around the outer periphery of the matrix and distal from the matrix bore 44 into which trapped gas can expand or be transferred. Gas trapped in the reservoir matrix when the matrix is initially charging with oil can escape into the peripheral volume created by the spacing regions 66 and bubbles generated during pumping can expand into the volume which provides a continuous pumping conductance at the periphery of the matrix which mitigates the effects of foaming. Since the reservoir matrix is no longer entirely constrained by the housing portion 30, the forces on the lubricant in the matrix are distributed both radially inwards and outwards, as shown by the horizontal arrows in Figure 6.
• the lubricant transfer arrangement 48 which in this example is an oil feed nut, is located radially inward of the reservoir matrix 62 in bore 44 and has an axis of rotation 22.
• the reservoir enclosure 30 is located radially outward of the reservoir matrix 62.
• the spacing regions 66 are located radially outward of the reservoir matrix around the outer periphery of the matrix.
• the spacing regions are separated from one another about the circumference by the contact regions 64, which are each located between adjacent spacing regions about the circumference.
• the spacing regions and contact regions may be uniformly distributed about the circumference or may be irregularly distributed. A uniform spacing is however preferred since it allows gas to escape relatively consistently from all regions of the matrix.
• the spacing regions are formed between an internal surface 70 of the reservoir enclosure and an external surface 72 of the reservoir matrix.
• both the internal surface of the reservoir enclosure and the external surface are cylindrical and have a circular cross- section. This arrangement does not provide a volume into which gas can escape from the matrix since the matrix is in intimate contact with the enclosure about its circumference.
• 10 and 1 1 the cross-section of the reservoir enclosure remains the same but the cross- section of the matrix is hexagonal to provide six contact regions and six spacing regions between the contact regions. Whilst a hexagonal cross-section is shown in Figure 5, 10 and 1 1 other polygonal or irregular cross-sections may be used to provide the required spacing regions for the expansion of gasses.
• the internal surface of the reservoir enclosure may have a polygonal or irregular cross-section whilst the external surface of the matrix may have a cylindrical cross-section, as shown in Figure 9.
• one of the internal surface of the reservoir enclosure or the external surface of the reservoir matrix may comprise channels for the passage of air or ridges to define spacing regions therebetween, as shown in Figure 8 and Figures 12a and 12b.
• at least one of the internal surface 70 of the reservoir enclosure 30, 54, or the external surface 72 of the reservoir matrix 62 comprise grooves 67, 80 respectively for forming at least some of the spacing regions.
• the grooves 80 are formed in the external surface 72 of the reservoir matrix 62 to provide the spacing regions 66 separated by contact regions 64 which, in use, contact the internal surface 70 of the reservoir enclosure 30.
• vertically extending axial grooves 80 are formed in the matrix 62.
• helical grooves 80 are formed, which provide a large surface area for air to escape the matrix 62.
• the reservoir matrix is formed of three layers, but more or less layers may be used, including forming the matrix 62 from a single piece of material.
• the width, W, of the grooves 80 are preferably sufficiently wide that if one of the layer rotates (for example due to contact with the bearing oil feed nut 48) that a continuous conductance is achieved between the layers along the grooves 80.
• grooves 78 are provided in the surface 78 of reservoir matrix 62 facing axially away from the bearing arrangement, i.e. towards the housing portion 54.
• the addition of the grooves 78, as shown in Figure 1 1 allows for the trapped air to escape downwards away from the reservoir matrix 62 and, when the turbomolecular pump is orientated horizontally (with the pump inlet facing upwards), for oil forced outwards from the reservoir to be captured in the base of the reservoir enclosure 30, 54.
• the grooves 78 can also be formed in the inwardly facing surface of the housing portion 54.
• the reservoir matrix 62 may also comprise a plurality of internal bores 74 formed between its internal 44 and external surface 50, said bores 74 extending axially between the axially upwardly, bearing facing surface of the matrix 62 and its axially downwardly facing surface 78 as shown in FIG. 10.
• Internal bores 74 in this sense are to be considered different from the porous structure of the reservoir matrix and considered to mean purposefully formed bores 74
• the internal bores 74 provide an additional space for the air contained in the reservoir matrix to escape, thus reducing the amount of oil foam reaching the bearing. It is also possible to use a reservoir matrix 62 with internal bores 74 instead of the spacing and contact regions 64, 66, but the combination of bores 74 and spacing/contact regions 64, 66 is preferably used because of their accumulative advantageous effects.
• the size (diameter, width etc.) of the bores 74 on respective layers are preferably sufficiently wide that if one of the layers rotates (for example due to contact with the bearing oil feed nut 48) that a continuous conductance is achieved between the layers along the bores 74 in respective layers.
• the spacing regions 66 extend axially over the length of the reservoir matrix 62.
• the cross-section of the matrix is uniform along the axial extent, although in other examples the cross-section may vary.
• the spacing regions are open at an axial end the upper of the matrix to allow gasses to be conducted away from the spacing regions. If the spacing regions were not open at least one axial end they would form pockets which trap gas rather than letting it be conducted away from the matrix.
• the provision of spacing regions in gas communication with volumes away from the matrix allows gas to be readily conducted and to reduce lubricant foaming.
• the reservoir matrix 62 is initially charged with lubricant such as oil. Any gas trapped during filling of the matrix can readily escape into the spacing regions 66, in addition to the bore 44 of the matrix, thereby reducing the propensity for lubricant foaming when the pump is in use.
• the motor 24 causes rotation of the turbo molecular pumping mechanism 14 and molecular drag pumping mechanism 16 about the axis of rotation 22.
• pressures between about 10 3 and 10 "7 mbar can be attained, and depending on the tolerances of the pump pressures as low as 10 10 mbar.
• Rotation of drive shaft 12 by the motor causes rotation of the lubricant transfer arrangement, or oil feed nut, 48.
• Lubricant is wicked from the reservoir matrix 62 along the finger projections 46 to the transfer arrangement and transferred to the bearing 26.
• the generation of vacuum pressures in the pump principally due to evacuation by a primary pump, generates a pressure differential across the reservoir matrix which induces bubble nucleation and outgassing in the matrix. Bubble nucleation can be accentuated by vibration caused by pump operation. Bubbles of gas are generated, in the matrix around nucleation sites, which increase in size.
• the spacing regions 66 located at the periphery of the matrix allow the gas bubbles to be dispersed reducing the occurrence of lubricant foaming detrimental to pump and bearing operation.
• - lubricant system/Lubricant transfer arrangement 42 - liquid lubricant reservoir 44 - central bore of the reservoir/matrix 46 - Projections (felt/brushes) 48 - tapered oil feed nut. 50 - external surface of the reservoir matrix 42. 52 - internal surface of the housing 30 54- housing portion (underneath reservoir matrix) 56 - bubbles 58 - lubricant foam 60 - lubricant supply system of the invention 62 - reservoir matrix 64 - contact regions

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Non-Positive Displacement Air Blowers (AREA)
• Rolling Contact Bearings (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)

Applications Claiming Priority (2)

Publications (2)

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Country Status (7)

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• 2013
  • 2013-04-22 GB GBGB1307196.4A patent/GB201307196D0/en not_active Ceased
• 2014
  • 2014-04-22 WO PCT/GB2014/051245 patent/WO2014174273A1/en not_active Ceased
  • 2014-04-22 CN CN201480022752.6A patent/CN105143682B/zh active Active
  • 2014-04-22 JP JP2016509544A patent/JP6402175B2/ja active Active
  • 2014-04-22 US US14/786,075 patent/US10190594B2/en active Active
  • 2014-04-22 EP EP14718727.2A patent/EP2989331B1/de active Active
  • 2014-04-22 CA CA2902049A patent/CA2902049A1/en not_active Abandoned

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